Process for recovering toluene



. ticable direct Patented Oct. 30, 1945 2,388,040 PROCESS FOB RECCVERINGTOLUENE Charles R. Clark, Springiield Township, Mont- Ailiell Che gomerrCounty, Pa., Dye Corporation, tion of New York- Application December 2In Canada Jul 17 Claims.

This ing toluene from organic liquids.

Numerous hydrocarbon oils are known which contain toluene in varyingproportions. For example, catalytic treatment of a suitable petroleumfraction in the presence of hydrogen, gives an oil consisting chiefly ofhydrocarbons of both aromatic and nonaromatic character, and containingabout 20% toluene. Gasoline fractions obtained by the distillation ofcertain types of petroleum frequently contain substantial proportions oftoluene, although mainly consisting of other hydrocarbons. Oil ofpetroleum origin having a considerable content of aromatics, includingbe treated by well known selectivesolvent processes to produce fractionsrich in aromatics; for example, extraction oi suitable fractions o! suchpetroleum oils with sulfur dioxide may yield fractions of high toluenecontent. In such cases toluene is accompanied by nonaromatic oils whichmay be largely paramnic, naphthenic `or cleilnic in character. Aconsiderable portion of these oils cannot be completely separated fromthe toluene by commercially pracfractional distillation methods becauseof the closeness of their boiling points to that of toluene or becausethey form constant boiling mixtures with toluene. Furthermore, whileordinarily toluene is readily separable by direct fractionaldistillation from light oils produced by the gasification of coal, insome cases the toluene is accompanied by difllcultly separablenon-aromatic oils of the same general character as described, owing tocarbonization conditions, type of coal used or other'specialcircumstances. Also synthetic hydrocarbon gas mixtures produced byvarious catalytic processes may contain toluene which, when recovered.is accompanied by similar diiiicultly separable constituents.

By fractional distillation oi these oils containing tolueneJractionsrelatively high in toluene content may be obtained. These tolueneiractions, however, will still contain large amounts of the other.constituents ci' the oil having boiling points in the neighborhood ofthe boiling point of toluene or forming mixtures of constant boilingpoints in the range oi' temperatures at which toluene distills from theoil. For example, by direct fractional distillation oi the abovedescribed types oi' oils containing toluene under the most emcientconditions commercially practicable for reotii'ying the vapors, afraction containing about 32% to 85% toluene appears to mixturescontaining it and other invention relates to a process for recover'assigner to New York, N. Y., a corporamical 0, 1941, Serial No. 423,185

' which contains, m addition to toluene,

represent a product of maximum toluene concentration obtainable.Accordingly, recovery oi' toluene of a relatively high purity from thesesources presents a difficult problem of great industrial importance.

For many purposes to which toluene is put, it is desirable to use aspure a material as may be economically available. For example, tolueneis largely used for the production of TNT, for which purpose aso-callednitration grade" of toluene is now preferred. While toluene productscontaining substantial proportions of certain hydrocarbon oils otherthan toluene can be nitrated, the mono-nitro compound made from themmust be purified prior to complete nitration. materially increases thecost and complexity of the process for making TNT. Furthermore, eventhough toluene containing substantial quantities of certain othermaterials is sometimes used for nitration, this is only because thedifculties of preparing a pure toluene have outweighed the disadvantagesof using the impure toluene for the production of explosives. Directfractional distillation, because of the diiiiculties pointed out above,will not effect a recovery of pure toluene from oils such as enumeratedand in many cases will not give fractions of suitably high toluenecontent or iree from materials which even in small concentrationsadversely affect the nitration of the toluene or the nitrated product.

It is an object of my invention to provide a process whereby toluene ofany desired degree oi purity may be recovered from oils containing itand other hydrocarbons which distill out over the same temperature rangeas the toluene.

In using my invention for the treatment o1 an oil such as has beendescribed above, containing toluene and other hydrocarbons, particularlywhen the toluene concentration of the oil is low or the oil is onecontaining materials of 'wide boiling range. I prefer first tofractionally distill the oil to remove highand low-boiling constituentsand to recover an enriched toluene fraction other hydrocarbons whichdistill at the same temperatures as the toluene. Although toluenefractions having an end boiling point substantially above the boilingpoint oi toluene (e. g. a' boiling point up to 118 C.) may beazeotropically distilled in the manner hereinafter described, 1' preferthe toluene fraction recovered in the preliminary distillation step beone having a maximum boiling point substantially corresponding to thebolling point of pure toluene; i. e., 111 C. Further, for the reasonswhich will be more specifically pointed out below, I prefer that thetoluene fraction recovered by the preliminary distillation oi' the crudetoluene oil be so cut as to exclude therefrom the iorerunnings which donot contain substantial proportions of toluene, for example, to excludeany materials distilling below 100 C.

A toluene fraction such as may be obtained by this preliminarydistillation, which may contain paramns, naphthenes, or oleiins, issubjected to a second distillation in the presence of a ketone in which=C=O is directly combined with both an unsubstituted ethyl radical andan unsubstituted alkyl radical containing no more more than 2 carbonatoms, preferably in the presence oi water. These materials may berepresented by the formula CxHs in which R is an unsubstituted alkylradical containing no more than 2 carbon atoms. 'I'he two members ofthis group are methyl ethyl ketone and diethyl ketone. I have discoveredthat when one of these ketones is mixed with a toluene fraction, such asis described above, and the mix ture is subjected to fractionaldistillation with rectification of the vapors in the presence of theketone and preferably also in the presence of water, non-toluenehydrocarbons present in the toluene fraction are selectively distilledfrom the mixture in the form of their azeotropes with the azeotropicagent to leave a residue containing toluene of desirable high puritywith respect to its content of other hydrocarbons originally present inthe toluene fraction and not separable from the toluene by directfractional distillation in the absence of the azeotropic agent. K

After the distillation has been carried to the Point at which theresidue containing toluene has the desired purity with respect tohydrocarbons distillinar from the toluene fraction in the sametemperature range as the toluene distills therefrom in the absence ofthe azeotropic agent. the distillation may be stopped and the residuewithdrawn from the still. Usually the toluene fraction subiected toazeotronic distillation in practicing this invention will be one havinga top boiling point not above 118 C. and preferably not above 111 C. Thetoluene fraction, theretore. will contain little, if any, hydrocarbonsboiling from the fraction ai temperatures above those at which tolueneboils therefrom. Accordingly, the residue withdrawn from the stillordlnarily will contain toluene and other hydrocarbons in the ratio oi95 or more parts toluene to 5 or less parts of total hydrocarbons otherthan toluene. It may be puriiled further, as desired, to remove anyazeotropic agent it contains and to remove any other impurities present.When the distillation is carried to the point at which all of theazeotropic agent has been distilled out of the residue and the tolueneconstitutes substantially 99% or more of the total hydrocarbon contentof the residue, the residue, which may be given a conventionaltreatment, for example. treatment with sulfuric acid. neutralization andredistillation, is suitable for marketing as a nitration grade tolueneof particularly high purity.

Instead of withdrawing the toluene residue from the still, thedistillation may be continued and the toluene distilled over andseparately collected from the distillate containing the hydrocarbonsfrom which the toluene residue previously has been separated byazeotropic distillation.

As stated above, ordinarily the toluene fraction treated in accordancewith my invention will contain little, if any, hydrocarbons distillingfrom the hydrocarbon-toluene fraction at temperatures above those atwhich toluene distills therefrom. On the other hand, it is not necessarythat such high boiling hydrocarbons always be excluded from the mixtureof azeotropic agent and toluene fraction subjected to distillation inaccordance with my invention. For example, one may desire toazeotropically distill a toluene oil from which all high boilinghydrocarbons have not been removed. In that case, the high boilinghydrocarbons may be left with the toluene residue at the conclusion ofthe azeotropic distillatlon of the toluene fraction under the conditionsset forth above to separate the toluene from the hydrocarbons of similarboiling range. After this separation has been effected, one may thenseparate the toluene from high boiling hydrocarbons present in theresidue by fractional distillation in the absence of the azeotropicagent.

My invention will be more particularly illustrated and described inconjunction with the following examples.

The accompanying drawing diagrammatically illustrates an apparatussuitable for carrying out the processes of these examples.

I'he apparatus o! the drawing comprises a still l provided with a heater2 and connected with a rectification column 3 and a condenser 4 for thevapors leaving the top of the column. By means or valves 5 and 6,condensate ilowing from condenser I is divided in controlledproportions. One part oi the condensate is returned through pipe 1 tothe top of column 3 and reiluxed in contact with the vapors rising inthe column. The other portion oi the condensate is withdrawn throughpipe B. Two receivers 9 and I0 are connected to pipe 8 throughvalve-controlled branch pipes Il and l2 so that the condensate drawn offthrough pipe B may be divided and distributed as de scribed below to thetwo receivers.

Receiver I0 is connected by a pipe I3 controlled by valve i4 with asecond still iB. Still i5, like still I, is provided with a heater I8, arectification column i1, a condenser l! and pipes i8 and 20 controlledby valves 2i and 22 for return oi' determined proportions of condensatefrom condenser I8 to the top of column I1 and Withdrawal of anotherportion of the condensate through pipe 20. Pipe 20 leads to a separator23 into which water may be introduced from a pipe 24. The separator isalso provided with a pipe 25 for withdrawal of an upper liquid layer anda pipe 2! for withdrawal of a lower liquid layer which may be i'ormedfrom the material treated in the separator, Suitable baffles may beprovided in separator 23 to facilitate continuous layer separation. Pipe28 leads to a liquid storage vessel 21. A pipe 28 controlled by valve 29permits introduction of liquid from storage vessel 21 into still I5. Apipe 30 controlled by valve 3i is also provided for introduction ofliquid into pipe 2B and thence into still Il. Pipe 32. controlled byvalve 33, permits introducing liquid directly into still IB. A pipe 34controlled by valve 3l leads from the bottom of still II to a separator30. Separator 30 is provided with a pipe 31 for withdrawal of an upperliquid layer. with a pipe 38 for withdrawal of a lower liquid layer anda pipe l! for introducing water into aasaoao 3 the separator. Suitablebellies may be provided in separator It to facilitate continuous layerseparation.

Example 1.-In carrying out one embodiment of my invention in theapparatus described above, a liquid hydrocarbon mixture containing about20% toluene, 20% of other aromatic hydrocarbons and the remaindersubstantially consisting of aliphatic and naphthenic hydrocarbons, withonly traces of oletlns, was introduced into still 1. This crude toluenematerial was produced by catalytic treatment or a petroleum distillatein the presence of hydrogen. It had a speciilc gravity of 0.760 at 15.5C. `and distilled over a range of from 56 C. to 161 C.

The charge of this hydrocarbon mixture introduced into still l wasboiled in the still and the evolved vapors were counter-currentlycontacted in column 3 with reflux from condenser l, in which the vaporsleaving the top of the column were substantially entirely condensed.Most of the condensate from condenser 4 was returned through valve i andpipe l to the top of the column to furnish the reilux for the column,the remaining. small portion oi' the condensate being continuouslywithdrawn through valve 0 and pipe l and passed into collecting vesselThe.

distillation was conducted under substantially atmospheric pressure; i.e., the pressure in condenser l and at the top ol' column 'I was subtstantially atmospheric and the pressure in still l was only enoughhigher to force the vapor through the rectification column to thecondenser.

When the vapor temperature in the top of column I reaches 109.5 C., thecondensate passing through pipe I is diverted to vessel l0. The

cut taken in vessel I0 includes the distillate coming over up to and ata temperature of 110.8 C. at the top of the column. After this cut hasbeen taken oi! to vessel I0, the distillation is discontinued and theresidue left in the still is withdrawn therefrom. The cut in vessel lcontains the low boiling fraction of the original oil. The residuewithdrawn from the still contains the high boiling components of thatoil. This fraction and residue may be treated or used in any desiredmanner.

Instead of discontinuing the distillation after ,the desired cut istaken-oi! to vessel il. the distillation may be continued and thecondensate passing forward through pipe I collected in a third vessel.not shown in the drawing, while the distillation is continued as long asmay be desired.` The cuts in vessel 0 and this third vessel contain lowand high boiling fractions of the original oil. 1i' the cut taken oi! tothe third vessel is limited to one containing substantial proportions oftoluene, e. g. up to 115 C. or 120' C., this cut may be redistilled orintroduced to still i with a subsequent batch of oil, and the toluene inthis cut recovered.

With edlcient rectification of the vapors in column 8 during thefractional distillation ci the crude toluene oil. the cut collected invessel Il contains about '16% by weight of toluene, as determined by thegpeciilc dispersion method for analyzing hydrocarbon oils described inIndustrial 8: Engineering Chemistry. Analytical Edition. vol. ll, page614, November 15, 1930.

The toluene fraction collected in vessel Il is 'aibiectec to anisotropicdistillation, which repthe second stage of this example. For thispurpose a charge con equal proportions by volume of methyl ethyl ketoneand the 16% toluene and 25H6 il! volume of water (based on the totalcharge of ketone and toluenefraction) is introduced into still ll.Distillation of this charge is started and water is fed to the bottomplate of rectification column I1 by an inlet pipe not shown in thedrawing as required to maintain at the top of the column a temperaturenot above 74 C. while permitting the vapors of aceotropes of thehydrocarbons to be removed from the toluene fraction being distilled topass out oi the rectification column to condenser I0. In distilling the76% toluene fraction under the foregoing conditions, the temperature atthe top of the rectiication column rose to '14 C. from an initialtemperature of about 12 C. By continuing the distillation thehydrocarbon residue remaining in the still after wash ing with waterwill contain 98-99% toluene. The distillate obtained in carrying out theprocess of this example may be extracted with water to separatelyrecover methyl ethyl ketone from hydrocarbons in the distillate.

The above procedure may be modified as follows:

The hydrocarbon residue left in still I8 by the azcotropic distillationis drawn from the still through pipe 3l to separator 3B in which theresidue is washed with water introduced through pipe 39 and then allowedto separate from the water. The bottom water layer is drawn oil throughpipe 38. The top layer, drawn oil through pipe 31, will contain Sii-99%toluene.

The distillate drawn oil to separator 28 sepa-' rates into two layers; atop vlayer high in hydrocarbons and low in methyl ethyl ketone and waterand a bottom layer high in methyl ethyl ketone and water and low inhydrocarbons. This bottom layer, constituting an aqueous methyl ethylketone solution, is drawn oil.' through pipe 2l to storage vessel 21 andin the aaeotropic distillation of a subsequent batch of the tolueneiraction, is introduced into the charge to still il for reuse of themethyl ethyl ketone as the azeotropic agent in this distillation.

In distilling a subsequent charge of toluene fraction in still IB withaddition thereto oi the aqueous solution of methyl ethyl ketone, noadditional water need be added over that contained in the solutionreturned from vessel 21. Thus, a quantity of water once introduced intothe distillation procedure may be largely retained therein andrepeatedly be used for extraction of the alcohol from the distillate andits return to the distillation step. Except for any make-up waterrequired to replace incidental losses from the system, no additionalwater generally is required. Additional water. however, may beintroduced into the distillate to increase the efficiency with which theazeotropic agent is extracted for return to the azeotropic distillationstep and water may be bled from the system in the toluene residue. fromthe base of the fractionating column, or otherwise removed from thesystem. Water may be mixed with the oil decanted through pipe 2l, themixture allowed to separate into layers, and

added to the aqueous solution in storage vessel 21 to increase theeffectiveness with which the methyl ethyl ketone is recovered from theoil distillate for reuse in the aseotropic distillation 75 ume ofdiethyl ketone and the '10% toluene fraction and 2/2% of water isintroduced into still I5 through pipes i3, 30 and 28. Distillation ofthis charge is started and water is fed to the bottom plate ofrectification column Il by an inlet pipe not shown in the drawing, asrequired to maintain at the top of the column a temperature not above 83C. while permitting the vapors of azeotropes of non-toluene hydrocarbonsto pass out of the rectication column to condenser I8. In distilling the'76% toluene fraction under the foregoing conditions, the temperature atthe top oi the recticaticn column rises to about 83 C. from an initialtemperature of about 79 C. By continuing the distillation the toluenecontent of the hydrocarbon residue remaining in the still, after washingwith water, will contain 98-99% toluene.

As in the process of Example 1, the distillate drawn off to separator 23separates into two layers; a top layer high in hydrocarbons and low indiethyl ketone and water and a bottom layer high in diethyl ketone andwater and low in hydrocarbons. This bottom layer, constituting anaqueous diethyl ketone solution, is drawn ofi' through pipe 26 tostorage vessel 2l and in the azeotropic distillation of a subsequentbatch of the toluene fraction, is introduced into the charge to still I5for reuse of the diethyl ketone as the azeotropie agent in thisdistillation.

By distilling a toluene fraction in accordance with the process ofExample 2 and the similar procedure of the modification o1' Example ldescribed above, the azeotropic agent used in the distillation of thetoluene fraction is recovered and returned to the distillation step in aparticularly effective, economical manner. 'I'he azeotropic agent isrecovered from the distillate by decantation and is reused 1n thedistillation of toluene fraction without costly dehydration steps. Onlythat amount of azeotropic agent required as make-up for any incidentallosses oi material need be continuously or periodically supplied to theprocess. Both methyl ethyl ketone plus water and diethyl ketone pluswater appear to form azeotropes with non-aromatic hydrocarbons oi' thetoluene distillation range. The ketones plus water have a goodselectivity for carrying over the non-aromatic hydrocarbons asdistillate and leaving toluene behind in the residue. At the same time,with Water present the ratio o1' hydrocarbons to azeotropic agent(ketone plus water) carried over into the distillate is increased ascompared with the anhydrous ketone. Accordingly, both for methyl ethylketone and for diethyl ketone, it is preferred to carry out thedistillation in the presence of water.

By my procedure substantially pure toluene, for example, a productcontaining about 99% or more toluene, readily may be recoveredcommercially from toluene fractions, such as described above, from whichpure toluene cannot be recovered practically by fractional distillationin the absence of an azeotropic agent. The products may be given aconventional treatment, for example, treatment with sulfuric acid,neutralization and redistillation, and they are then Suitable formarketing as a nitration grade toluene of particularly high purity.

Example 3.-In fractionally distilling the hydrocarbon mixture containingabout toluene described above, the portion distilling between 107.5" C.and 110 C. was separately collected. 100 volumes of this fraction i 68volume toluene) were charged together with 250 volumes of methyl ethylketone and 100 volumes of water into still 15 and fractionally distilledwith rectication of the vapors in a column Il of about 36 equivalenttheoretical plates. The vapors leaving the top of the column werecondensed in condenser I8. Fifteen to 20 parts of the condensate werereturned through pipe I9 to the top of column I1 to 1 part o1' thecondensate which was withdrawn by pipe 20 to separator 23. Thetemperature oi' the vapors at the top of the column rose from an initialvalue of 71.7 C. to '73.4 C. During the course of the distillation anadditional 100 volumes of the ketone and 50 volumes of water were added.When the methyl ethyl ketone had been exhausted about oi the tolueneavailable was obtained in the distillation residue as toluene of about94% (by volume) purity.

Example 1 -The process of this example was used for the treatment of atoluene fraction having a boiling range of approximately 108 C. to 111C. and containing about '10% by volume toluene.

A charge of this toluene fraction and diethyl ketone in equalproportions by volume was distilled in a still I 5 and the vaporsrectied in rectiiication column I1 with condensation o! the vapors incondenser I8, return of redux through pipe i9 and withdrawal ofdistillate through pipe 20. Most of the non-aromatic hydrocarbons in theoil were selectively distilled over at temperatures up to 107.6'J C.,leaving a residue of which the hydrocarbon content was 92% by volumetoluene. r

The diethyl ketone employed in the distillation procedure of thisexample had the particular advantage of carrying over in the distillate'with the non-aromatic hydrocarbons a very small ratio Aof toluene tonon-aromatic hydrocarbons. Thus, the initial distillates coming on attemperatures up to 100.5 C. contained no toluene and the succeedingdistillate coming over from 100.5 C. to 101.0 C. contained only 4%toluene based on the oil content of the distillate.

Example 5.-A charge of the same toluene fraction as was distilled by theprocess oi' Example 4 was introduced into still I 5 together with anequal volume o1' diethyl ketone and hall' as much water. Distillationstarted with the temperature of the vapors at the top oi therectification column at 80.8 C. When this'vapor temperature had risen to82.7 C. and the fraction coming over at this temperature contained about88% by volume toluene based on the oil content of the distillate, thedistillation was discontinued. The residue was washed with water toremove diethyl ketone. 'Ihe oil layer which separated from the aqueousextract contained 92% by volume toluene.

Numerous changes and modifications may be made in the above describedprocesses without departing from my invention. While in the rstdistillation step of the crude toluene oil it is preferred to take oi atoluene fraction having an end boiling point of substantially 111 C. andfractions with a higher end boiling point, such as 118 C., may besuccessfully distilled azeotropically to obtain pure toluene, even alarger leeway is permitted in the temperature at which the toluenefraction starts to be taken oi; i. e., in the initial boiling point ofthe toluene fraction. Nevertheless, it is preferred that the toluenefraction subjected to azeotropic distillation be one boiling in therange of C. to 111 C Such a fraction tropic distillation may bedistilled in the azeostep of my process and pure toluene obtained with arelatively small quantity of azeotropic agent present during thedistillation. Pure toluene may be obtained by distllling with theazeotropic agent a toluene fraction boiling, for example, from 95 C. to118 C., but the quantity of azeotropic agent present in thedistillatlonof the toluene fraction of wider boiling range must besubstantially increased as compared with the quantity which suffices fordistilling the fraction of the narrower boiling range.

While I have described my process in conjunction with examples in whichthe two distillation steps are batch procedures, either or both of thesedistillations advantageously may be carried out continuously by wellknown continuous distillation procedures suitable for the fractionaldistillation of mixtures of two or more liquids.

The minimum ratio of azeotropic agent to the toluene fraction which issuitable for carrying` out my invention will vary with the particularagent used, the amount and nature of the hydrocarbon impurities in thetoluene fraction, the purity distillation, the proportion oi toluene inthe original toluene fraction which is to be recovered in the residuefrom the distillation, and the procedure used for the azeotropicdistillation. The ratios of the above examples are suitable for a batchprocess carried out according to the procedures of the examples.However, it is preferred to employ even higher ratios oi azeotropicagent to toluene fraction than in some of the examples, e. g. Example l.In the process of that example the methyl ethyl ketone may be exhaustedfrom the distillation column before in the residue is tls-99% toluene.Although this high toluene content of the residue is obtained in theprocess of this example by continued distillation with temperaturesrising above '14 C'. after the methyl ethyl ketone is exhausted, it ispreferred to have present in the distillation suificient methyl ethylketone so that when the desired purityl of hydrocarbon in the residue isattained there is still some of the methyl ethyl ketone therein.Irrespective of the particular batch or continuous procedure used,therefore, the quantity of aneotrcpic l tlllation of hydrocarbons from agiven quantity of toluene fraction is preferably in excess of that whichwill forin azeotropic mixtures with the non-toluene hydrocarbons whichare to be vaporized and taken over into the distillate. This quantityoi' azeotropio agent includes fresh agent introduced into the materialbeing distilled and also any of the azeotropic agent Vwhich may beseparated from the distillate and returned continuously or periodicallyto the still or rectiflcation column while the distillation of thetoluene fraction is pro. Temperature readinsstaken ofthevaporatthetopofthe rectification column provide a particularly good theprocess with respect to C. Methyl ethyl ketone an Diethyl ketone 102Methyl ethyl ketone and water Dlethyl ketone and water.-....-

the hydrocarbon desired in the toluene residue from the.

agent used in the dis- By supplying additional azeotropic agent (eitherketone or water or both) to prevent this temperature from exceeding theabove temperatures, an adequate amount of azeotropic agent will bepresent during the separation of the nontoluene hydrocarbons from thetoluene fraction. It is not necessary that this point oi controltemperature be at the top of the column, although this is a satisfactorypoint for determining this temperature in the equipment used forfractionating the vapors and condensing the fractionated vapors 1n theabove examples for effective use of the rectification column. Oneskilled in the distillation art will recognize suitable points formaintaining this control temperature in any other speciilc apparatusaccording to well known distillation principles.

It is, of course, obvious that preliminary distillation of a crudetoluene oil to obtain a toluene fraction suitable for recovery oftoluene therefrom by the azeotroplc distillation need not be carried outin immediate conjunction with the azeotropic distillation. The toluenefraction may be produced in one plant, transported to and treated laterin another plant to azeotropically distill it. Nor is my inventionlimited to any particular procedure for the production of the toluenefraction. My invention contemplates distilling with methyl ethyl ketoneor diethyl ketone, preferably with water, any oil containing toluenetogether with other hydrocarbons which, when the oil is distilled,vaporize therefrom in the same temperature range as the toluene and,therefore, are not separable from the toluene by direct fractionaldistillation. As used in this specification and the appended claims, theterm toluene fraction" refers to all such toluene-containing oils,whether produced by fractional distillation of toluene-containingmaterials or by any other means.

In this speciiication I have described the azeotropic distillation oftoluene fractions as carried out under substantially atmosphericpressure. The temperatures as given in this specification and in theappended claims are corrected temperatures for one atmosphere pressure(760 mm. of Hg). It is, of course, possible to azeotropically distillthe toluene fraction under pressures above or below atmospheric. In thatcase-the temperatures will differ from the temperatures given herein dueto the changes in boiling points caused by the change in pressure.

I claim:

1. The process for the recovery of toluene from a toluene fractioncontaining the same and oontaining non-aromatic hydrocarbons boilingfrom said fraction in the same temperature range as the toluene boilstherefrom which comprises azeotropically distilling said toluenefraction in the presence of a ketone having the formula in which R is anunsubstituted alkyl radical containing no more than 2 carbon atoms, andthereby vaporizing said ketone and non-aromatic hydrocarbons present insaid toluene fraction. said ketone being present in amount sulcient toseparate selectively from said toluene fraction nonaromatlc hydrocarbonspresent therein which distill therefrom in the absence of said ketone inthe same temperature range as toluene contained therein and to carryover said non-aromatic hydrocarbons with vapors of said ketone, leavinga lwdrocarbon residue of the distillation enriched in toluene.

2. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons boilingfrom said fraction in the same temperature range as the toluene boilstherefrom which comprises azeotropically distilling said toluenefraction in the presence of water and a ketone having the formula inwhich R is an unsubstituted alkyl radical containing no more than 2carbon atoms, and thereby vaporizing said ketone and non-aromatichydrocarbons present in said toluene fraction, said ketone being presentin amount sufficient to separate selectively from said toluene fractionnonaromatic hydrocarbons present therein which distlll therefrom in theabsence of said ketone and water in the same temperature range astoluene contained therein and to carry over said non-aromatichydrocarbons with vapors oi' said ketone and water, leaving ahydrocarbon residue of the distillation enriched in toluene.

3. I'he process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons whichdistill from the toluene fraction in the same temperature range as thetoluene distills therefrom, which comprises distilling said toluenefraction inthe presence of a ketone having the formulaL ClHs in which Ris an unsubstltuted alkyl radical containing no more than 2 carbonatoms, thereby vaporlzing said ketone and non-aromatic hydrocarbonspresent in said toluene fraction, said ketone being present in amountsufiicient to separate selectively from said toluene fractionnonaromatic hydrocarbons present therein which dis-- aqueous solutionthus obtained for the azeotropic distillation of a toluene fractioncontaining nonaromatic hydrocarbons which distill from the toluenefraction in the same temperature range as the toluene distillstherefrom.

4. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons boilingfrom said fraction in the same temperature range as the toluene boilstherefrom which comprises azeotropically distilling said toluenefraction in the presence of' methyl ethyl ketone and thereby va-Dorizing said ketone and non-aromatic hydrocarbons present in saidtoluene fraction, said ketone being present in amount sufficient toseparate selectively from said toluene fraction non-aromatichydrocarbons present therein which distill therefrom in the absence ofsaid methyl ethyl ketone ln the same temperature range as toluenecontained therein and to carry over said non-aromatic hydrocarbons withvapors of said ketone and water, leaving a hydrocarbon residue of thedistillation enriched in toluene.

5. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons boilingfrom said fraction in the same temperature range as the toluene boilstherefrom which comprises azeotropically distilling said toluenefraction in the presence of methyl ethyl ketone and water and therebyvaporizing said ketone and non-aromatic hydrocarbons present in saidtoluene fraction, said ketone being present in amount suilicient toseparate selectively from said toluene fraction non-aromatichydrocarbons present therein which distill therefrom in the absence ofsaid methyl ethyl ketone and water in the same temperature range astoluene contained therein and to carry over said non-aromatichydrocarbons with vapors of said ketone and water, leaving a hydrocarbonresidue of the distillation enriched in toluene.

6. The process for the treatment of a toluene fraction to separate thetoluene from non-aromatic hydrocarbons contained therein which dis tillfrom the toluene fraction in the same temperature range as the toluenedistills therefrom, which comprises distilling said toluene fraction andrectifying the vapors evolved therefrom in the presence of methyl ethylketone and water in amount such that at a point in the rectification ofthe vapors temperatures not substantially above 7 4 C. are maintainedwhile vaporizlng and removing from said toluene fraction hydrocarbonspres- 4 ent therein which distill therefrom, in the absence of saidketone and water, in the same temperature range as toluene containedtherein.

7. The process for the treatment of a toluene fraction having an endboiling point not above 118 C. and containing paraiinic hydrocarbons,and which may also contain naphthenic and olefinic hydrocarbons, theaforesaid hydrocarbons distilling from the toluene fraction in the sametemperature range as the toluene boils therefrom, which comprisesdistilling said toluene fraction and rectifying the vapors evolvedtherefrom in the presence of methyl ethyl ketone and water in amountsuch that at a point in the rectification of the vapors a temperaturenot substantially above 74 C. is maintained until the unvaporizedresidue of the distillation contains at least parts by weight of tolueneto every 5 parts by weight of other hydrocarbons, and thereby vaporizingand selectively removingfrom said toluene fraction hydrocarbons presenttherein which distili therefrom, in the absence of said ketone andwater, in the same temperature range as toluene contained therein.

8. The process for the recovery of toluene from a crude toluene oilproduced by catalysis of a petroleum fraction in the presence ofhydrogen which comprises recovering from said crude oil a toluenefraction having an end boiling point of 111 C. containing paratilnic andnaphthenic hydrocarbons, and which may'also contain olefinichydrocarbons, which hydrocarbons distill from said toluene fraction inthe same temperature range as the toluene distills therefrom, distillingsaid toluene fraction and rectifying the vapors evolved therefrom in thepresence of methyl ethyl ketone and water in amount such that at a pointin the rectification of the vapors a temperature not above 74 C. ismaintained until the unvaporized residue of the distillation containstoluene separated from like-boiling, non-aromatic hydrocarbons whichwere present in said toluene fraction.

9. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons whichdistill from the toluene fraction in thesame temperature range as thetoluene distills therefrom, which comprises distilllng said toluenefraction and rectifying the vapors evolved therefrom in the presence ofwater and methyl ethyl ketone, thereby vaporizingsaid ketone andnon-aromatic hydrocarbons present in said toluene fraction, said ketonebeing present in amount suillcient to separate selectively from saidtoluene fraction non-aromatic hydrocarbons present therein which distilltherefrom, in the absence of said methyl ethyl ketone and water, in thesame temperature range as toluene contained therein and to carry oversaid non-aromatic hydrocarbons with vapors of said ketone and water,leaving a hydrocarbon residue of the distillation enriched in toluene,condensing the vapors thus distilled from said toluene fraction to forma liquid distillate, extracting said distillate with water, separatingthe resulting aqueous layer from the hydrocarbon oil layer, andemploying the aqueous layer thus obtained, containing methyl ethylketone in solution, for the azeotropic distillation of a toluenefraction containing non-aromatic hydrocarbons which distill from thetoluene fraction in the same temperature range as the toluene distillstherefrom.

l0. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons whichdistill from the toluene fraction in the same temperature range as thetoluene distills therefrom, comprises distilling said toluene fractionin the presence of water and methyl ethyl ketone thereby vapcrizing anddistilling over a. mixture of vapors of methyl ethyl ketone, water andhydrocarbons present in said toluene fraction which distill therefrom,in the absence of methyl ethyl ketone and water, in the sametemperaturerange as toluene contained therein, said ketone being presentin amount suilicient to separate selectively said non-aromatichydrocarbons from said toluene fraction and to carry over thenon-aromatic hydrocarbons with the vapors of said ketone and water,leaving a hydrocarbon residue oi the distillation enriched in toluene,cooling said mixture of vapors to condense them and form a liquidcontaining two phases, an ous phase containing methyl ethyl ketone and ahydrocarbon oil phase, separating the aqueous phase from the hydrocarbonoil, and employing the aqueous solution of methyl ethyl ketone thusobtained for the azeotropic distillation of a toluene fractioncontaining non-aromatic hydrocarbons which distill from the toluenefraction in the same temperature range as the toluene distills Ytherefrom.

1l. The process for the recovery or toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons boilingfrom said fraction in the same temperature range as the toluene boilstherefrom, which comprises azeotropically distillins said toluenefraction ln the presence of diethyl ketone and thereby vaporising saidketone and non-aromatic hydrocarbons present in said toluene fraction,said ketone being present in amount suillcient to separate selectivelyfrom said toluene fraction non-aromatic hydrocarbons present thereinwhich dlstill therefrom in the absence of said diethyl ketone in thesame temperature range as toluene contained therein and to carry oversaid non-aromatic hydrocarbons with vapors o! said ketone, leavin: a

hydrocarbon residue of the distillation enriched in toluene.

l2. The process for the recovery oi toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons boilingfrom said fraction inthe same temperature range as the toluene boilstherefrom, which comprises azeotroplcally distilling said toluenefraction in the presence of diethyl ketone and water, and therebyvaporizing said ketone and non-aromatic hydro- Carbons present in saidtoluene fraction, said ketone being present in amount suillcient toseparate selectively from said toluene fraction non-aromatichydrocarbons present therein which distill therefrom in the absence ofsaid diethyl ketone and water in the same temperature range as toluenecontained therein and t0 carry over said nonaromatic hydrocarbons withvapors of said ketone and water, leaving a hydrocarbon residue of thedistillation enriched in toluene.

13. The process for the treatment of a toluene fraction to separate thetoluene from non-aromatic hydrocarbons contained therein which distillfrom the toluene fraction in the same temperature range as the toluenedistills therefrom, which comprises distilling said toluene fractionevolved therefrom in the presence of diethyl ketone and water in amountsuch that at a point in the rectification of the vapors temperatures notsubstantially above 83 C. are maintained while vaporizing and removingfrom said toluene fraction hydrocarbons present therein which distilltherefrom, in the absence of said ketone and water, in the sametemperature range as toluene contained therein.

14. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons whichdistill from the toluene fraction in the same temperature range as thetoluene distills therefrom, which comprises distilling said toluenefraction and rectifying the vapors evolved therefrom in the presence ofWater and diethyl ketone, thereby vaporizing said ketone andnon-aromatic hydrocarbons present in said toluene fraction, said ketonebeing present in amount sulcient to separate selectively from saidtoluene fraction non-aromatic hydrocarbons present therein which distilltherefrom, in the absence of an azeotropic agent, in the sametemperature range as toluene contained therein and to carry over saidnon-aromatic hydrocarbons with vapors of said ketone and water, leavinga hydrocarbon residue of the distillation enriched in toluene,condensing the vapors thus distilled from said toluene fraction to forma liquid distillate, extracting said distillate with water, separatingthe resulting aqueous layer from the hydrocarbon oil layer, andemploying the aqueous layer thus obtained, containing diethyl ketone insolution, for the azeotropic distillation of a toluene fractioncontaining non-aromatic hydrocarbons which distill from the toluenefraction in the same temperature range as the toluene distillstherefrom.

l5. The process for the recovery of toluene from a toluene fractioncontaining the same and containing non-aromatic hydrocarbons whichdistill from the toluene fraction in the same temperature range as thetoluene distills therefrom, which comprises distilling said toluenefraction in the presence of water and diethyl ketone, thereby vaporizingand distilling over a mixture of vapors of diethyl ketone, water andnon-aromatic hydrocarbons present in said toluene fraction which distilltherefrom, in the absence oi the diethyl ketone and water. in the sametemperature range as toluene contained therein, said ketone beingpresent in amount sumcient to separate selectively said non-aromatichydrocarbons from said toluene fraction and to carry over thenon-aromatic hydrocarbons with the vapors of said ketone and water,leaving a hydrocarbon residue of the distillation enriched in toluene,cooling said mixture of vapors to condense them and iorm a liquidcontaining two phases, an aqueous phase containing diethyl ketone and ahydrocarbon oil phase, separating the aqueous phase from the hydrocarbonoil, and employing the aqueous solution of diethyl ketone thus obtainedfor the azeotropic distillation of a toluene fraction containingnen-aromatic hydrocarbons which distill from the toluene fraction in thesame temperature range as the toluene distills therefrom.

16. A process for the treatment o! a toluene fraction to separatetoluene therefrom from the hydrocarbons contained therein whichordinarily distill from the hydrocarbon fraction in the same temperaturerange as said toluene distills therefrom which comprises distllling saidtoluene fraction in the presence of a sumcient amount of methyl ethylketone to vaporize hydrocarbons other than said toluene together withmethyl ethyl ketone thereby leaving said toluene in the residuesubstantially completely separated from the hydrocarbons other than saidtoluene.

17. A process for the treatment of a toluene fraction to separatetoluene therefrom from the hydrocarbons contained therein whichordinarily distill from the hydrocarbon fraction in the same temperaturerange as said toluene distills therefrom which comprises distilllng saidtoluene iraction in the presence of a sulcient amount o1' methyl ethylketone containing water to vaporize hydrocarbons other than said toluenetogether with methyl ethyl ketone and water thereby leaving said toluenein the residue substantially completely separated from the hydrocarbonsother thansaid toluene.

CHARLES R. CLARK CERTIFICATE OF C ORRECTI ON Patent No. 2,588,0iio.

October 50, 19145.

CHARLES R. CLARK.

It is hereby certified that error appears in the printed specification'of the above numbered patent requiring correction as follows: Page 6,second column, line l, strike out the words "and waterm; and that thesaid letters Patent should be read with this correction therein that theseme may conform to the record of the case in the Patent Office.

signed and `sealed this 29th day of January, A. o. 19Li6.

(Seal) Leslie Frazer First Assistant Commissione:- of Patents.

and water. in the same temperature range as toluene contained therein,said ketone being present in amount sumcient to separate selectivelysaid non-aromatic hydrocarbons from said toluene fraction and to carryover the non-aromatic hydrocarbons with the vapors of said ketone andwater, leaving a hydrocarbon residue of the distillation enriched intoluene, cooling said mixture of vapors to condense them and iorm aliquid containing two phases, an aqueous phase containing diethyl ketoneand a hydrocarbon oil phase, separating the aqueous phase from thehydrocarbon oil, and employing the aqueous solution of diethyl ketonethus obtained for the azeotropic distillation of a toluene fractioncontaining nen-aromatic hydrocarbons which distill from the toluenefraction in the same temperature range as the toluene distillstherefrom.

16. A process for the treatment o! a toluene fraction to separatetoluene therefrom from the hydrocarbons contained therein whichordinarily distill from the hydrocarbon fraction in the same temperaturerange as said toluene distills therefrom which comprises distllling saidtoluene fraction in the presence of a sumcient amount of methyl ethylketone to vaporize hydrocarbons other than said toluene together withmethyl ethyl ketone thereby leaving said toluene in the residuesubstantially completely separated from the hydrocarbons other than saidtoluene.

17. A process for the treatment of a toluene fraction to separatetoluene therefrom from the hydrocarbons contained therein whichordinarily distill from the hydrocarbon fraction in the same temperaturerange as said toluene distills therefrom which comprises distilllng saidtoluene iraction in the presence of a sulcient amount o1' methyl ethylketone containing water to vaporize hydrocarbons other than said toluenetogether with methyl ethyl ketone and water thereby leaving said toluenein the residue substantially completely separated from the hydrocarbonsother thansaid toluene.

CHARLES R. CLARK CERTIFICATE OF C ORRECTI ON Patent No. 2,588,0iio.

October 50, 19145.

CHARLES R. CLARK.

It is hereby certified that error appears in the printed specification'of the above numbered patent requiring correction as follows: Page 6,second column, line l, strike out the words "and waterm; and that thesaid letters Patent should be read with this correction therein that theseme may conform to the record of the case in the Patent Office.

signed and `sealed this 29th day of January, A. o. 19Li6.

(Seal) Leslie Frazer First Assistant Commissione:- of Patents.

